1. The Field of the Invention
The present invention relates to the manufacture of semiconductor circuit devices. More particularly, the present invention is directed to methods for reducing encroachment of the field oxide into the active area on a silicon integrated circuit.
2. Technology Review
The conventional LOCOS (local oxidation of silicon) technique is often used to define active regions and isolation or field oxide regions of a silicon wafer. In the LOCOS process, a silicon substrate or wafer is oxidized to form a thin gate oxide layer comprising SiO.sub.2. A silicon nitride pattern is formed on the gate oxide layer and the silicon substrate is further oxidized. The nitride layer inhibits diffusion of oxygen whereas the gate oxide allows oxygen diffusion. As a result, the silicon substrate which is not protected by the nitride layer is oxidized to form field oxide regions. As used herein, the term "oxide" refers to silicon dioxide (SiO.sub.2).
A significant problem with this technique for forming field oxide regions and active regions is that the field oxide encroaches under the nitride layer into the active region, thereby reducing the area of the active region. The encroachment represents wasted space on the final semiconductor circuit device. Any technique which is able to reduce the amount of wasted space on the semiconductor circuit without compromising performance would open the possibility for even further miniaturization of the semiconductor circuit device.
Attempts have been made in the art for reducing encroachment of the field oxide into the active region. One process, known as the SWAMI technique, addresses the problem of encroachment of the field oxide. In the SWAMI technique, a silicon nitride pattern is deposited on the gate oxide layer as in the conventional LOCOS technique, but rather than oxidize the silicon substrate, the gate oxide and silicon substrate are etched. Thereafter, a second gate oxide layer is formed where the substrate had been etched and a nitride layer and an oxide layer are deposited over the entire substrate. The outer nitride and oxide layers are subsequently anisotropically etched, and the substrate is oxidized to form the field oxide regions.
Although the SWAMI technique is effective at reducing the encroachment of the field oxide, it tends to damage the underlying silicon substrate. Hence, processes for producing semiconductor circuit devices using the SWAMI technique have low yields. Moreover, because the SWAMI technique can require as many as six or seven additional processing steps, it is not widely used in the industry.
From the foregoing, it will be appreciated that what is needed in the art are methods for reducing encroachment of the field oxide into the active area on a silicon integrated circuit.
Additionally, it would be a significant advancement in the art to provide methods for reducing the encroachment of the field oxide into the active area which do not add a significant number of additional processing steps.
Finally, it would be an important advancement in the art to provide methods for reducing the encroachment of the field oxide into the active area on a silicon integrated circuit which does not damage the silicon substrate.
Such methods for reducing encroachment of the field oxide into the active area on a silicon integrated circuit are disclosed and claimed herein.